Sliding vane rotary pumps have a multitude of mechanical and industrial applications and as such are exposed to a wide range of environmental conditions. In one particular application, sliding vane rotary pumps are utilized in a aircraft where the pumps are exposed to severe atmospheric conditions consisting of widely varying partial pressures of natural film-forming atmospheric constituents such as water vapor and oxygen. During such exposure, parts of the pump experience undue wear that tends to lead to possible pump failure.
Heretofore, the component parts of rotary pumps were manufactured from carbon material as disclosed in U.S. Pat. No. 3,191,852 issued to Kaatz, et al. on Jun. 29, 1965. These carbon parts are fabricated by compressing carbon, graphite and various organic binders under high pressure and temperature. Unfortunately, carbon parts manufactured in this manner exhibit very little tensile strength and tend to fail in an erratic manner. Frictional contact between moveable and stationary parts in pumps operating under extreme atmospheric conditions results in deteriorating wear adversely affecting the operational capabilities of the pump. Furthermore, the fragile nature of carbon parts occasionally results in chipping or fracture of the part during use this requiring repair and/or replacement.
To address the limitations of carbon parts, rotary pump manufacturers have proceeded in two different directions. First, as disclosed in U.S. Pat. No. 4,804,317 issued to Smart, et al. on Feb. 14, 1989, a carbon composite material has been used for the side plates and vanes of the rotary pump. A composite carbon part is fabricated by combining carbon based tensile strength fibers (in a cloth weave) with graphite and an organic binder. Although providing improved performance over the prior carbon parts, similar wear, chipping and fracture problem exist with composite carbon parts. Second, as disclosed in U.S. Pat. No. 4,820,140 issued to Bishop on Apr. 11, 1989, a self-lubricating coating has been applied to the pump parts to inhibit wear between the slidable vanes and pump rotor. The coating is comprised of a mixture of lead and polytetrafluoroethylene deposited on the surface of the part to be coated.